The present invention relates to a method for die casting the end rings and conductor bars on and in a stack of laminations to thereby form a rotor for use in an electric motor. The invention is related to the automatic loading apparatus disclosed in patent application Ser. No. 115,770 filed Jan. 25, 1980, now U.S. Pat. No. 4,271,895 and entitled Automatic Part Loader Unit for Multi-Cavity Rotor Die and Method of Operation. This patent is expressly incorporated herein by reference.
In the manufacture of squirrel cage rotors for electric motors, it is common practice to form them of a plurality of stacked, circular laminations each having a central opening and a plurality of openings positioned in a circular array near the peripheral edge of the lamination. The laminations are stacked on a stacking pin with the peripheral openings aligned, either along axes parallel to the central axis of the stack, or with a slight skew from one lamination to the next so that the openings collectively form a plurality of partially helical passages or channels axially through the stacked laminations.
These rotor preforms are then loaded into the die cavities of a die casting machine, and molten aluminum is injected into the cavities whereupon it flows through the channels in the stacked laminations to form the conductor bars and end rings on opposite ends of the stack of laminations, which provide electrical interconnection between the conductor bars. The end rings may either be formed smooth or with fins for the purpose of cooling. The formed rotors are then removed from the die casting machine, and the stacking pins are pressed out so that the rotor assembly is held together by means of the cast aluminum end rings and conductor bars.
In the past, the lamination stacks have been hand loaded directly into the die cavities through the parting line of the separated die plates. The die plates were then closed and a shot of molten aluminum or other suitable metallic material injected into the die cavities to form the conductor bars and end rings. Subsequently, the die plates were opened and the cast rotors removed by hand and transported to the pin press out station.
Later, automatic die casting machines were developed whereby the lamination stacks could be automatically loaded and retrieved from the die cavities, and the stacking pins were pressed out with the cast rotors still in the retriever. The loader moved laterally between the separated dies from one side of the compensating mechanism, and following casting, the retriever moved between the parting line of the die plate from the other side of the compensating mechanism. Although this eliminated manual handling of the lamination stacks and rotors, the process is quite cumbersome and requires a large amount of floor space. This is because the flow of material is generally linear through the machine with the stacked lamination preforms being loaded laterally from one side of the compensator-casting plunger axis and being retrieved from the opposite side thereof. Thus, two operators for the machine were necessary, one to load the stacked lamination preforms into the machine and the other to retrieve the cast rotors. Since the pressed out pins are immediately recycled to form new stacked lamination preforms, they must either be transported around to the opposite side of the die casting machine where the stacking pin press is located, or, if the pin press is located on the discharge side of the machine, then the stacked lamination preforms themselves must be transported around to the loading side of the machine.